The crude bathroom in the dingy cellar where Fritzl allegedly kept his family captive

TERROR DEN: The tiny 'cell' hid a wealth of horrors

CHILLING: The secret entrance to the dungeon

It is impossible even to begin to imagine what they have gone through. Their story is beyond belief.

DI Franz Polzer

Evil Josef Fritzl, 73, yesterday admitted he locked his daughter in a windowless dungeon for 24 years, continuously raped her and fathered seven children with her.

As the sickening story unfolded in Austria, it emerged that three of the children had never seen daylight until last week.

Three others were raised by Fritzl and his wife Rosemarie, 60, who is said by police to have been totally unaware of the family living in the sealed-off cellar.

Another child, one of a pair of twins born in 1996, died shortly after birth and was burned by Fritzl.

Austrian police released pictures of the multi-roomed dungeon, which was accessed via an electronically-locked concrete door, hidden behind a shelf.

Rosemarie was last night at a psychiatric hospital being reunited with her traumatised daughter, who has white hair and very pale skin after being deprived of daylight for so many years.

In 1984, when Elisabeth was just 18, engineer Fritzl drugged her and handcuffed her in the cellar.

She was reported missing, but police called off the search after her father forced her to write a letter telling officers she did not want to be found.

While life got back to normal on the surface, twisted Fritzl was creating a second family with his daughter underneath his house in Amstetten.

In 1989, Elisabeth gave birth to Kerstin, now 19, followed by Stefan, 18, Lisa, 15, Monika, 14, Alex, 12, and Felix, five. Fritzl acted as “midwife”.

Kerstin, Stefan and Felix lived with their mum, now 42, in the dungeon. The other three were planted on his doorstep by Fritzl, who claimed his “lost” daughter dumped them there to be adopted.

The trio lived with Fritzl and Rosemarie’s own six children, not knowing their mum and siblings were hidden below.

The dungeon contained washing and cooking facilities and a TV, the captives’ only contact with the outside world.

Soundproofing made it impossible for the outside world to hear any cries for help.

Electronics expert Fritzl told his daughter the cellar was wired to a bomb, which would explode if they tried to escape.

The horrific crime only emerged after Kerstin fell into a coma. Fritzl took her to hospital and doctors launched a TV appeal for her mum to come forward, believing the illness was genetic.

The sick engineer then panicked and released Elisabeth and her other children, claiming they had “returned home”.

Elisabeth told all to police after they promised that she would not have to see her father again.

She told officers Fritzl started abusing her when she was just 11.

Doctors are now running medical tests on the three children who have never seen daylight, fearing their skin and eyes may be permanently damaged.

They and their mother are said to be in a terrible mental and physical state. Detective Inspector Franz Polzer, leading the investigation, said: “It is impossible even to begin to imagine what they have gone through. Their story is beyond belief.”

Josef was in custody last night as Austrian authorities prepared to haul him in front of a judge.

The country is still reeling from the 2006 case of Natasha Kampusch, now 20, who escaped from a dungeon where she had been held as a sex slave for eight years by Wolfgang Priklopil, 44.